In recent years, mobile communication terminals, in particular, have been provided with more advanced functions in association with the advancement and proliferation of wireless communication modes. In addition, due to the proliferations of mobile terminals compatible with both domestic and international services, wireless LAN, and the like, it has been required that one wireless communication apparatus should be compatible with two or more wireless communication modes. Moreover, the frequency bands used by various wireless communications tend to become closer in association with the progress of the effective use of frequencies.
Conventionally, when two or more wireless communication modes are operated in a single wireless communication apparatus, a transmission wave of a certain mode raises the noise floor of the reception band of another mode. This phenomenon has deteriorated the reception sensitivity of another communication mode.
Specifically, in a multimode communication apparatus that incorporates a plurality of components (communication units) each provided with a transmitter unit and a receiver unit, degradation in wireless communication characteristics occurs mutually when the respective units are operated at the same time. When one of the units transmits a radio wave, the transmission wave raises the noise floor of the reception band in another system, degrading the reception sensitivity of the other system(s), in particular, in the case that the frequency bands used by the wireless communication modes of the units are close to one another. That is, the frame error rate (FER) and the bit error rate (BER), for example, increase.
In order to resolve such a problem, it is conceivable to provide the transmitter section of each of the units with various filters, such as variable frequency stop filter, band pass filter (BPF), and band elimination filter (BEF) (see Patent Document 1).
Nevertheless, since various filters such as mentioned above have high attenuation, transmission waves that pass through the filters suffers from great loss. Moreover, if another unit with a different wireless communication mode is added, it will become necessary to add a filter that is compatible with the frequency band of that system. Such addition of the filter brings about further power loss in pass band and an increase in size of the apparatus. An increase in power loss in pass band results in a shorter wireless communication distance and a narrower communication area.
Patent Document 1: JP-A-2004-222171
The present invention relates to a multimode communication apparatus that uses a plurality of wireless communication modes, and particularly, it is an object of the invention to provide a multimode communication apparatus that can suppress adverse effects that a transmission wave under one mode has on the communications of other modes.